"Wait" I thought, "does this mean Parapluvo could mean umbrella", using the best of my french-knowledge. I looked it up, but it appeared the chosen words were 'Pluvombrelo' which I felt was too excessive. But the thoughts continued "What.. if I would call it Propluvo, as in 'because of rain' or 'for rain'. It's genious!".
I vote that we call umbrella Propluvo. And a parasol will then be Prosuno, obviously, instead of Sunombrelo.
So how would you distinguish between an umbrella and a raincoat? Or a beach umbrella and a sunburn (which you got "because of the sun")?
According to Lernu, that means both the ones you use against the sun, and the rain. It appears this is a very English-like solution, as the best translation for Parasol came up as "Beach umbrella".
In Swedish we use Paraply and Parasol. Against-rain and Against-sun. Hence my vote. :)
kontraŭsuna aŭ kontraŭpluva ombrelo
The umbrella is not for, but against the sun or the rain.
Or simply: sunombrelo, pluvombrelo.
I figured kontraŭ would come up as an alternative. I considered it, but I figured it sounded weird. Propluvo sounded better. And unless I'm completely lost in prepositions Pro is synonymous with 'Because of' which I think is just as good as 'Against'.